Hydrotreating is a process to catalytically stabilize petroleum products and/or remove undesirable substances from hydrocarbon products or feedstocks by reacting them with hydrogen. Suitable hydrocarbon feedstocks vary widely from naphtha to reduced crude oils. The objectives of hydrotreating include (1) converting unsaturated hydrocarbons to saturated hydrocarbons (for example, olefins and diolefins to paraffins) and (2) removing undesirable substances such as sulfur, nitrogen, oxygen, halides and trace metals from the feedstock.
Generally in hydrotreating processes, the hydrocarbon feedstock is mixed with hydrogen-rich gas either before or after the feedstock is preheated to the proper temperature. The feedstock is typically preheated from about 500.degree. F. to about 800.degree. F. The feedstock enters a reactor in the presence of a metal-oxide catalyst. The hydrogen reacts with the feedstock to form hydrogen sulfide, ammonia, saturated hydrocarbons and free metals. The metals remain on the surface of the catalyst and the other products leave the reactor with the hydrocarbon-hydrogen stream. The hydrocarbon-hydrogen stream then enters a separator to separate the hydrocarbon from the hydrogen-rich gas. The hydrocarbon is stripped of any remaining hydrogen sulfide and "light ends" in a stripper. The gas stream is treated to remove hydrogen sulfide.
As described above, refinery processes (such as separating and converting) typically involve preheating of the hydrocarbon feedstocks. Preheating is normally accomplished by using heat exchangers in which a series of metal tubes carrying the hydrocarbon are encased in a second tube which carries a hot stream. The heat from the stream is conducted through the tubes to the hydrocarbon feedstock which is then carried to the next stage of processing. The hydrocarbon feedstocks, which may be unrefined or partially refined, are generally preheated to temperatures in the range of about 300.degree. F. to about 1,600.degree. F. The specific preheated temperature will depend upon the temperature and physical phase requirements of further processing.
One of the major problems encountered during hydrocarbon processing, and particularly in heating equipment, is fouling. The term "fouling" as used herein refers to the formation of deposits on the metal surfaces of processing equipment. Fouling deposits most frequently occur at elevated temperatures and vary in composition as organic, inorganic, or mixed organic and inorganic deposits. The organic deposits are primarily insoluble, high molecular weight, polymerization products. The inorganic deposits frequently contain silica, iron oxide, iron sulfide, alkaline earth metal oxides, and various metal salts. Inorganic portions are believed to result from ash components of the crude oil, corrosion products from the metal surfaces that the feedstock contacts, and contaminants from the various metallic catalysts used in processing.
The efficiency of processing equipment is materially decreased when fouling occurs. The direct results of fouling appear in the form of heat transfer loss, increased pressure drop between the heat exchanger equipment inlet and outlet, and loss in-throughput. When fouling deposits accumulate, the equipment sometimes must be disassembled and mechanically and/or chemically cleaned to remove the deposits, or in extreme cases, the equipment must be completely replaced. Consequently, the processing units must be shut down, resulting in lost production.
Fouling deposits from hydrotreater units often contain substantial amounts of iron sulfide. The iron sulfide deposits originate from active corrosion in wellbores, pipelines, or crude oil storage facilities. Particulate iron sulfide entrained in the hydrocarbon precipitates in the hydrocarbon/effluent exchanges. The iron sulfide is believed to act as a deposit binder, thereby increasing the fouling rate. If the deposition of iron sulfide can be inhibited, fouling will be reduced significantly. This is readily accomplished by use of the dispersant antifoulants described in the present invention.